Climate Change Will Not Spare an Inch of Global Ocean, Study Finds

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Every corner of the world's oceans — from pole to pole and sea
surface to seafloor — will undergo chemical changes associated
with global climate change by 2100, jeopardizing the livelihoods
of billions of people who subsist on marine ecosystems, according
to a new study.

Previous studies addressing the effects of climate change on
future ocean health have tended to focus on the effects of
increased temperature and acidity on marine ecosystems. However,
other oceanic conditions — including dissolved oxygen and
productivity, or the abundance of
tiny plant-like organisms that form the base of the marine
food web — also play an important role in overall ocean health.
As is the case on land, marine animals need oxygen and plant-life
to survive. [ Video:
Humans Hit the Oceans Hard ]

A team of 29 international scientists based at the University of
Hawaii, Honolulu, have now developed more comprehensive
projections of future ocean health, which take into account
temperature, acidity, dissolved oxygen and productivity. To
develop these projections, the researchers compiled more than
80,000 existing modeled maps of oceanic change, many of which
informed the latest
Intergovernmental Panel on Climate Change (IPCC) report.

The team found that mangrove and coral reef ecosystems near the
tropics will likely experience the smallest cumulative change by
2100, whereas cetaceans (the group of mammals that includes
whales,
dolphins and porpoises), as well as pinnipeds (such as seals and
walruses) will face the largest amount of change.

"We already knew that coral reefs are very susceptible to
temperature change, and our models show that they are going to be
impacted the least," study co-author Camilo Mora, a researcher at
the University of Hawaii, Honolulu, told LiveScience. "So you can
imagine what it's going to be like for other ecosystems."

The team used the compiled maps to estimate the impact these
changes will have on coastal human populations whose livelihoods
depend on marine resources.

Researchers considered two different climate change scenarios:
one in which humans significantly cut back carbon dioxide
emissions and, as a result, global atmospheric carbon dioxide
levels increase from the current 440 parts per million (ppm) to
just 550 ppm; and one in which humans continue emitting carbon
dioxide at the current rate, under a scenario known as "business
as usual," which
the IPCC projects will result in an atmospheric carbon
dioxide accumulation of 900 ppm by the end of the century. (Parts
per million is an indicator of the concentration of a chemical
in, for example, air. So in this case, 440 ppm means that there
are 440 molecules of carbon dioxide in every million molecules of
air.)

Under the 550-ppm scenario, the team estimated that 1.4 billion
people would face considerable local oceanic change by 2100. Of
those people, 690 million will live in countries with medium to
high ocean dependence — a metric the researchers developed of the
extent to which a society's jobs, revenue and food depend on the
ocean.

Under a business-as-usual scenario, 2 billion people will face
considerable oceanic change by 2100, with 1.12 billion of them
living in countries with medium to high dependence on the ocean.
Of those 2 billion people, 870 million will live in low-income
countries with few resources to adapt to the projected changes.

The team notes that these estimates are rough, and that the
specific ways in which ecosystems and communities adjust to
change will remain largely unknown until the changes unfold.

Mora likens this uncertainty to the uncertainty of falling off of
a ladder: Some sort of injury is inevitable, but the exact body
part or degree of injury remains unpredictable until a person
hits the ground.

"Systems are very complex," Mora said. "You can't tell what
species are going to go extinct, or the response of a specific
species, but you can expect these changes to be quite massive."

The researchers hope to continue synthesizing new data as it
becomes available, in order to continue honing the precision of
their predictions.

The new findings are detailed today (Oct. 15) in the journal PLOS
Biology.